fix mathjax version to 3.1.2, 3.1.4 fails

Author: linev

package.json

@@ -25,7 +25,7 @@
     "d3": "^6.1.1",
     "gl": "^4.6.1",
     "jsdom": "^16.4.0",
-    "mathjax": "^3.1.2",
+    "mathjax": "3.1.2",
     "three": "^0.121.0",
     "xhr2": "^0.2.0",
     "zlib": "^1.0.5",